@tschk/crepuscularity-wasm

The crepuscularity parser, compiled to WebAssembly. This is the same Rust code that backs the crepus CLI — not a reimplementation — so JavaScript consumers and native targets lower templates identically.

import { parseCrepus, IR_VERSION } from "@tschk/crepuscularity-wasm";

const ir = parseCrepus(`div flex flex-col gap-4\n  span text-lg\n    "hello"`);
// { version: 7, root: [ { kind: "stack", ... } ] }

Template variables are bound by passing a context object. String, finite number, boolean, and null values retain their types for expression evaluation. Non-finite numbers (NaN and infinities) throw TypeError instead of becoming JSON null:

parseCrepus('span\n  "hello {name}"', { name: "Ada" });

parseCrepus and parseTemplate reject source strings and filenames containing unpaired UTF-16 surrogates with TypeError before WebAssembly encoding can replace them. Valid astral characters and literal replacement characters are preserved.

Other syntaxes

parseTemplate picks a frontend from the filename, so .crepus, .jsx/.tsx, .svelte, .vue, .astro, and Angular component templates (*.component.html, *.ng.html, *.ng) all compile to the same View IR:

import { parseTemplate } from "@tschk/crepuscularity-wasm";

parseTemplate('<div class="flex"><span>{t}</span></div>', "Panel.svelte");
parseTemplate("<template><div class=\"flex\">{{ t }}</div></template>", "Panel.vue");

These are first-party frontends: neither svelte nor vue is a dependency. They compile the template. A <script> block is extracted and its semantics — Svelte runes, Vue's composition API, stores, lifecycle — are not executed; expressions are evaluated by crepuscularity's own evaluator. A construct the shared AST cannot represent is a parse error rather than a silent drop.

View IR

parseCrepus returns a ViewIr, a versioned tree of ViewNodes. Every node carries the original template class tokens on style.classes, so web renderers can pass them straight through as className instead of re-deriving CSS from the lowered style hints.

Check IR_VERSION if you persist or transport IR — the schema is versioned and bumps on incompatible changes.

Browsers and workers

The root entry is synchronous and uses the Node/Bun loader. For browsers or module workers, load the explicit browser entry first:

import { loadParser } from "@tschk/crepuscularity-wasm/browser";

const { parseTemplate, IR_VERSION } = await loadParser();
const ir = parseTemplate("<p>Hello</p>", "Panel.svelte");

Initialization is shared, including failures. Parsing is synchronous after loading; use this entry inside a worker to keep parsing off the UI thread. Serve browser/crepuscularity_wasm_bg.wasm relative to the bundled entry, or pass its served URL to the first loadParser(url) call when your bundler relocates assets. The browser entry has the same validation and context limits as the root entry.

Run the real Chromium/WebKit worker acceptance test after building with python3 browser.test.py (requires installed Python Playwright browsers).

Building

Requires the wasm32-unknown-unknown target and a wasm-bindgen CLI matching the wasm-bindgen crate version, plus Bun for the smoke tests. From this npm directory, run bun run test after rebuilding the bindings.

../build.sh

The build honors CARGO_TARGET_DIR, including paths containing spaces. Cargo and wasm-bindgen use the same resolved target directory.

If the shell selects a compiler whose sysroot lacks the WASM target while rustup's selected compiler has it installed, select that compiler explicitly:

RUSTC="$(rustup which rustc)" ../build.sh